Liquid crystal display device having particular stacked layered structure at peripheral portion

ABSTRACT

For preventing corrosion of signal lines (conductive layers for supplying signals to pixel areas) which are formed over one of a pair of substrates of a liquid crystal display device and are disposed so as to extend from the inside of an area surrounded by a sealing material toward the outside of the area, that at least one of the signal lines is covered with stacked layers formed of a first insulating film, a semiconductor layer, and a second insulating film formed sequentially over the at least one of the signal lines in this order.

BACKGROUND OF THE INVENTION

The present invention relates to a liquid crystal display device inwhich it is possible to avoid corrosion of the signal lines thereof

A liquid crystal display device includes a panel made of substratesdisposed so as to be opposed to each other with a liquid crystalinterposed therebetween, and the display device is provided withnumerous pixels disposed in a matrix arrangement over the area of theliquid crystal. In the case of a reflection type of liquid crystaldisplay device, at least one of the pair of substrates is a transparentsubstrate; whereas in the case of a transmission type of liquid crystaldisplay device, both substrates are transparent substrates. The term“transparent substrate” used herein is not limited to a substrate inwhich tight absorption does not at all occur, but encompasses asubstrate which allows light propagating through the liquid crystal tobe transmitted through the substrate at an intensity sufficient toenable a user of the liquid crystal display device to recognize an imagereproduced by the propagating light. A transmission type liquid crystaldisplay device will be described below by way of example.

Means for generating an electric field which corresponds to a videosignal is incorporated into each pixel arranged on theliquid-crystal-side (or the liquid-crystal-layer-side) of the mainsurface of one of the pair of transparent substrates, whereby theoptical transmissivity of the liquid crystal can be controlled accordingto the strength of the electric field. For this reason, signal lineswhich supply signals to the respective pixel areas are formed over theliquid-crystal-side main surface of the one of the pair of substrates,and these signal lines are disposed to extend outward of the panel.

Specifically, the one transparent substrate (the substrate over whichthe signal lines are formed) of the pair of transparent substratesconstituting the panel is constructed to be slightly larger in area thanthe other transparent substrate, and the signal lines are disposed so asto extend into the area of the one transparent substrate which extendsbeyond the other substrate (in other words, the area of the onetransparent substrate which protrudes beyond and is not overlapped bythe other transparent substrate, and these signal lines are connected toan external circuit.

Incidentally, a sealing material is arranged in a portion equivalent tothe periphery of the other transparent substrate, whereby the othersubstrate is fixed to the one transparent substrate. These transparentsubstrates are combined so that a predetermined gap is maintainedbetween the main surfaces thereof, and the liquid crystal is sealed inthe gap. Concretely, a region surrounded by the sealing material isformed in a space lying between the pair of substrates, and this regionforms a space for containing the liquid crystals.

SUMMARY OF THE INVENTION

However, in, the liquid crystal display device constructed in the mannerdescribed above, it has been formed that disconnections due to corrosionoccasionally will occur in the signal lines which extend from the insideof the region surrounded by the sealing material (the area in which theliquid crystal is sealed) to the outside thereof A technique for solvingthe problem of corrosion of the signal lines is described in, forexample, each of Japanese Patent Application Laid-Open Nos. 326942/1999,113922/1997 and 90394/1997.

The signal lines which extend from the inside of the area surrounded bythe sealing material have heretofore been covered with a film formed byexpanding a protective film, disposed in a display area comprising anassembly of pixels, to the edge portions of the substrates (hereinafterreferred to as the expanded film). The present inventors have carriedout research to determine why the above-described corrosion of thesignal lines occurs even in a liquid crystal display device having thisconstruction, and have found that, if there is a defect, such as apinhole in the expanded film, a signal line disposed below the defectiveportion tends to corrode.

In recent years, the distance between a signal line and another signalline adjacent thereto is becoming smaller and the electric fieldstrength therebetween is becoming larger, so that there is a strongerpossibility that the above-described corrosion of the signal lines willbe promoted. In addition, even if no disconnection occurs, there is nodenying the fact that the corrosion of a signal line may reach thebottom of a sealing material, so that a leakage hole may be produced inthe sealing material and a leakage defect of the liquid crystal mayoccur.

The present invention has been made on the basis of the above-describedcircumstances, and an object of the present invention is to provide aliquid crystal display device which is capable of preventing corrosionfrom occurring in signal lines which are formed to extend from inside anarea of a main surface of one of a pair of substrates into an outsidearea, the inside area being generally surrounded by a sealing material(an area opposed to a liquid crystal layer).

A representative aspect of the invention disclosed in the presentapplication will be described below in brief

The liquid crystal display device of the present invention has a pair ofsubstrates disposed to oppose one another with a liquid crystalinterposed therebetween; a plurality of pixel areas formed over aliquid-crystal-side surface of one of this pair of substrates; and aplurality of signal lines for respectively supplying signals to theaforementioned plurality of pixel areas being formed over theliquid-crystal-side surface of the one of this pair of substrates, whichsignal lines extend beyond a seating material for fixing this pair ofsubstrates to one another and toward a peripheral portion of the one ofthis pair of substrates; and at least one of the plurality of signallines is covered with stacked layers formed by stacking a firstinsulating film, a semiconductor layer, and a second insulating filmthereover in this order.

In this manner, the signal lines which are formed to extend beyond thesealing material are covered with the stacked layer made of the firstinsulating film, the semiconductor layer and the second insulating film.Accordingly, even if defects, such as pinholes, occur in each of thefirst insulating film, the semiconductor layer and the second insulatingfilm, it will be extremely rare for the portions of the defects to besuperposed on one another on the signal lines, and so almost no externalinfluence is exerted over the signal lines due to these defects. In thisway, it is possible to avoid corrosion due to defects, such as pinholes,in the material which covers the signal lines.

In the construction described above, each of the aforementionedplurality of pixel areas is provided with a thin film transistor coveredwith a protective film, and the first insulating film, the semiconductorlayer and the second insulating film are formed of materials which areidentical to those of a gate insulating film and a semiconductor layer,both of which constitute elements of the thin film transistor, and theprotective film covering the, thin film transistor, respectively.

In this case, since the first insulating film, the semiconductor layerand the second insulating film can be sequentially formed in parallelduring formation of each of the pixels, there is the advantage that thepresent invention can be implemented without any increase in the numberof manufacturing steps.

These and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing one embodiment of the liquidcrystal display device according to the present invention;

FIG. 2 is an equivalent circuit diagram showing one embodiment of theliquid crystal display device according to the present invention;

FIG. 3A is a plan view and FIG. 3B is a section view taken of the lineb—b in FIG. 3A, showing one embodiment of the construction of a pixel ofthe liquid crystal display device according to the present invention;

FIG. 4 is a perspective view showing the vicinity of the driver ICconnected to signal lines of the liquid crystal display device in oneembodiment according to the present invention;

FIGS. 5A and 5B are a cross-sectional views showing other examples ofthe liquid crystal display device according to the present invention;

FIGS. 6A and 6B are cross-sectional views showing other examples of theliquid crystal display device according to the present invention; and

FIG. 7 is a cross-sectional view showing another example of the liquidcrystal display device according to the present invention.

DETAILED DESCRIPTION

Embodiments of a liquid crystal display device according to the presentinvention will be described with reference to the drawings.

Embodiment 1 Equivalent Circuit of Liquid Crystal Display Device

FIG. 2 is an equivalent circuit diagram showing one embodiment of aliquid crystal display device according to the present invention. FIG. 2is a circuit diagram which is depicted to correspond to an actualgeometrical arrangement.

In FIG. 2, there is shown a liquid crystal display panel 1. This liquidcrystal display panel 1 has a pair of transparent substrates disposed soas to be opposed to each other with a liquid crystal interposedtherebetween, and scanning signal lines 2 and video signal lines 3 areformed over a liquid-crystal-side surface of a transparent substrate 1A,which is one of the pair of transparent substrates. The scanning signallines 2 are disposed so as to extend in the x direction of theliquid-crystal-side surface and to be juxtaposed in the y directionthereof, while the video signal lines 3 are insulated from the scanningsignal lines 2 and are disposed so as to extend in the y direction andto be juxtaposed in the x direction. Incidentally, the x direction andthe y direction as referred to herein intersect with each other, and theintersection angle therebetween is herein defined as an angle which isnot limited to a right angle.

The rectangular areas which are each surrounded by adjacent ones of thescanning signal lines 2 and adjacent ones of the video signal lines 3constitute pixel areas, respectively, and a thin film transistor TFT anda pixel electrode 5 are formed in each of the pixel areas. A thin filmtransistor TFT is turned when it receives a scanning signal from one ofthe scanning signal lines 2, and this causes a video signal to besupplied to a pixel electrode 5 from one of the video signal lines 3 viathe thin transistor TFT which is turned on. This pixel electrode 5 ismade of a transparent material, for example, comprises an ITO(Indium-Tin-Oxide) layer. A capacitance element Cadd is formed betweenthe pixel electrode 5 and the other scanning signal line 2, and anelectric charge corresponding to the video signal supplied to the pixelelectrode 5 can be stored in the capacitance element Cadd for acomparatively long time.

Although not shown, a common electrode which is common to each of thepixel electrodes and is made of a transparent material is formed on aliquid-crystal-side surface of the other transparent substrate 1B whichis disposed over the transparent substrate 1A constructed in thismanner, with the liquid crystal interposed therebetween. The opticaltransmissivity of the liquid crystal between this common electrode andthe pixel electrode 5 is controlled by an electric field generatedtherebetween.

A scanning signal is supplied to one end of each of the scanning signallines 2 via an external terminal by a vertical scanning circuit 7. Thisvertical scanning circuit 7 is formed of plurality of driver ICs whichare mounted on the transparent substrate 1A in a facedown manner. Theoutput electrode of the vertical scanning circuit 7 is connected to theexternal terminal. Similarly, a video signal is supplied to one end ofeach of the video signal Lines 3 from a video signal driver circuit 8via an external terminal. This video signal driver circuit 8 is formedof plurality of driver ICS which are mounted on the transparentsubstrate 1A in a facedown manner, and the output electrode of thevideo, signal driver circuit 8 is connected to the external terminal.

In each of the areas where the vertical scanning circuit 7 and the videosignal driver circuit, 8 are respectively mounted, the edge of thetransparent substrate 1B is constructed to be set back from the edge ofthe transparent substrate 1A. Specifically, the transparent substrate 1Bis formed to be slightly smaller in area than the transparent substrate1A, and it is disposed in such a manner that its right and bottom sidesare in substantial alignment (preferably, coincide) with those of thetransparent substrate 1A. The vertical scanning circuit 7 and the videosignal driver circuit 8 are mounted on the area of the transparentsubstrate 1A that projects from the transparent substrate 1B.

Pixel Area

FIG. 3(A) is a plan view showing one embodiment of the construction ofthe above-described pixel area, and FIG. 3(B) is a cross-sectional viewtaken along tine b—b of FIG. 3(A).

In FIG. 3(A), the scanning signal lines 2 which are disposed so as toextend in the x direction and to be juxtaposed in the y direction areformed over the transparent substrate 1A, and an insulating film 4 isformed over the entire surface of the transparent substrate 1A to coverthe scanning signal lines 2. This insulating film 4 functions as aninterlayer insulating film for the scanning signal lines 2 with respectto the video signal lines 3 which will be formed later. In addition, inthe area in which the thin film transistor TFT is formed, the insulatingfilm 4 functions as a gate insulating film. Moreover, in the area inwhich the capacitance element Cadd is formed, the insulating film 4functions as a dielectric film.

The pixel electrode 5 is formed over the surface of the insulating film4, and this pixel electrode 5 is a transparent electrode made of, forexample, an ITO (Indium-Tin-Oxide) film. This pixel electrode 5 isformed in such a manner that a portion thereof is superposed on one ofthe scanning signal lines 2 (the upper signal line as viewed in FIG.3A), and this portion of the pixel electrode 5 constitutes thecapacitance element Cadd, in which a dielectric film made of theinsulating film 4 is disposed between the scanning signal lines 2 andthe pixel electrode 5.

The area in which the thin film transistor TFT is formed is disposed tobe superposed on the other scanning signal tine 2 (the lower signal lineas viewed in FIG. 3A), and an island-shaped semiconductor layer 6 madeof, for example, amorphous Si is formed in that area. A drain electrode3 d and a source electrode 3 s are formed over the surface of thesemiconductor layer 6, thereby forming an MIS type of transistor havinga gate electrode made of a portion of the scanning signal line 2. Thedrain electrode 3 d and source electrode 3 s are formed together withthe video signal lines 3.

Specifically, the video signal lines 3 which are disposed so as toextend in the y direction and to be juxtaposed in the x direction areformed, and part of each of the video signal lines 3 is formed to extendto the surface of the area in which the thin film transistor TFF isformed, thereby forming the drain electrode 3 d.

The source electrode 3 s which is formed at the same time as the drainelectrode 3 d is disposed so as to extend into the pixel area so as tobe connected to the pixel electrode 5 which is formed in advance.Moreover, a protective film 9 made of, for example, a silicon nitridefilm is formed over the entire surface of the substrate processed inthis manner, and an alignment; layer 10 for restricting the orientationof the liquid crystal is formed over the top surface of the protectivefilm 9.

The pixel area formed in this manner is constructed so that the thinfilm transistor TFT is driven by a scanning signal supplied from thescanning signal line 2, causing a video signal from the video signaltine 3 to be supplied to the pixel electrode 5 via this thin filmtransistor TFT. If the thin film transistor TFT is turned off, the videosignal supplied to the pixel electrode 5 can be stored in thecapacitance element Cadd for a long time.

Construction in the Vicinity of Driver IC

FIG. 4 is a perspective view showing the construction in the vicinity ofdriver ICs 7A and 8A mounted on the transparent substrate 1A, and is aview as seen from the side indicated by arrow IV in FIG. 2.

A plurality of driver ICs, 7A which constitute the vertical scanningcircuit 7 are mounted along the y direction on the y-direction side (asviewed in FIG. 4) of the transparent substrate 1A, which is projectedfrom the transparent substrate 1B, while a plurality of driver ICs 8A,which constitute the video signal driver circuit 8, are mounted alongthe x direction on the x-direction side (as viewed in FIG. 4) of thetransparent substrate 1A. For example, the plurality of driver ICs 7Aare arranged so that a respective one of the driver ICs 7A is assignedto each of a predetermined number of groups of adjacent scanning signallines 2.

Each of the scanning signal lines 2 is formed so as to extend from thepixel areas into the portion of the transparent substrate 1A over whichthe transparent substrate 1B is not formed, and is connected at one endto the output terminal of a driver IC 7A. The input terminals of thedriver ICs 7A are connected to an interconnection layer formed in aperipheral portion of the transparent substrate 1A (in many cases, anedge portion of the substrate), and this interconnection layer issupplied with a signal from a flexible printed circuit board JT2.Incidentally, a similar construction is also provided on the side of thedriver, ICs 8A which constitute the video signal driver circuit 8. InFIG. 4, the input terminal of any of the driver ICs 7A and 8A is coveredwith a film FL which is printed with the output terminal of the flexibleprinted circuit board JT2 or FPC.

FIG. 1 is a view showing a cross section taken along line I—I of FIG. 4.In FIG. 1, the scanning signal line 2 which is disposed so as to extendfrom the surface of the transparent substrate 1A beyond the edge of thetransparent substrate 1B is formed on the top surface of the transparentsubstrate 1A, and the extended end of the scanning signal line 2 isconnected to an output terminal 12 of the driver IC 7A, which isdisposed in a faced down manner. This scanning signal line 2 is coveredwith a stacked layer formed by stacking the insulating film 4, thesemiconductor layer 6 and the protective film 9 thereon in that order.

The insulating film 4, semiconductor layer 6 and protective film 9correspond to the insulating film 4, the semiconductor layer 6 and theprotective film 9 in each of the pixels, respectively. This stackedlayer is formed so as to extend over the scanning signal line 2 from aliquid crystal layer LC (inside a sealing material 13) beyond aperipheral portion of the transparent substrate 1B (outside the sealingmaterial 13), and the end portion of the stacked layer is formed toreach the area of the driver IC 7A and to extend only to the vicinity ofthe output terminal 12. In other words, this stacked layer is formed soas not to make contact with that portion of the scanning signal line 2which comes in direct contact with the output terminal of the driver IC7A (a portion which serves as a signal input terminal).

Incidentally, the transparent substrate 1B is fixed to the transparentsubstrate 1A by the sealing material 13 formed on the protective film 9.This sealing material 13 has the function of maintaining the gap betweenthe transparent substrate 1A and the transparent substrate 1B at apredetermined value and of sealing the liquid crystal in the gap. Anorganic resin 14 is applied between the transparent substrate 1A and thetransparent substrate 1B outside the sealing material 13. An organicresin 15 is applied between the transparent substrate 1A and the driverIC 7A on the side of the output terminal 12 of the driver IC 7A. Theseorganic resins 14 and 15 are formed to improve the reliability of theseal to prevent corrosion or the hole of the underlying scanning signalline 2. A similar construction is also provided in the vicinity of thedriver ICs 8A on the video signal lines 3.

In this manner, the scanning signal lines 2 (or the video signal lines3) which are formed to extend beyond the sealing material 13 are coveredwith a stacked layer formed of the insulating film 4, the semiconductorlayer 6 and the protective film 9. Accordingly, even if defects, such aspinholes, occur in one or all of the insulating film 4, thesemiconductor layer 6 and the protective film 9, it is extremelyunlikely that the portions of the defects will be superposed on oneanother on the scanning signal lines 2, and it can be expected inpractice that almost no such portions will be superposed. For thisreason, it is possible to avoid corrosion due to defects, such aspinholes, in a material which covers the scanning signal lines 2 (thevideo signal lines 3).

In addition, since the insulating film 4, the semiconductor layer 6 andthe protective film 9 can be sequentially formed over each of the pixelsand, at the same time, over the scanning signal lines 2, which extendinto the peripheral portion of the substrate, there is the advantagethat the number of manufacturing steps does not need to be increased topractice the present invention.

Embodiment 2

FIG. 5A is a view showing the construction of another embodiment of theliquid crystal display device according to the present invention, and isa view similar to FIG. 1. The construction of FIG. 5A differs from thatof FIG. 1 in that the stacked layer formed by sequentially stacking theinsulating film 4 and the semiconductor layer 6 is not formed at alocation where the sealing material 13 is formed. In other words, thestacked layer is formed so as to extend from outside the sealingmaterial 13 to the side of the driver IC 7A. In this case, theprotective film 9 is formed to extend directly from inside the sealingmaterial 13 in a manner similar to that shown in FIG. 1.

The reason for this construction is to ensure a predetermined flatnessat the location where the sealing material 13 is formed, and to improvethe uniformity of the gap between the transparent substrate 1A and thetransparent substrate 1B. In this case, it is possible to fully avoidcorrosion of the scanning signal line 2 in the vicinity of the sealingmaterial 13 owing to the presence of the organic resin 14.

Embodiment 3

FIG. 5B is a view showing the construction of another embodiment of theliquid crystal display device according to the present invention, and isa view similar to FIG. 1. The construction of FIG. 5B differs from thatof FIG. 1 in that the stacked layer formed by sequentially stacking theinsulating film 4 and the semiconductor layer 6 on the scanning signalline 2 is formed to extend from a position halfway below the sealingmaterial 13 to the side of the driver IC 7A. Specifically, the outsideportion of the sealing material 13 (on the peripheral side of thetransparent substrate 1A) is formed in such a manner that the stackedlayer formed by sequentially stacking the insulating film 4 and thesemiconductor layer 6 is interposed between a portion of the sealingmaterial 13 and the scanning signal line 2, but the insulating film 4and the semiconductor layer 6 do not extend all of the way under thesealing material 13 (on the side of the liquid crystal LC). In thiscase, the protective film 9 is formed to extend directly from inside thesealing material 13 in a manner similar to that shown in FIG. 1.

The reason for this construction is to obtain an effect having both theeffect of strengthening the corrosion-preventing effect for the scanningsignal line 2 and the effect of flattening the location where thesealing material 13 is formed.

Embodiment 4

FIG. 6A is a view showing the construction of another embodiment of theliquid crystal display device according to the present invention, and isa view similar to FIG. 1. The construction of FIG. 6A differs from thatof FIG. 1 in that the stacked layer formed of the insulating film 4, thesemiconductor layer 6 and the protective film 9 is formed to extendhalfway into the output terminal 12 of the driver IC 7A. Specifically,the side of the output terminal 12 that faces the sealing material 13 isformed in such a manner that the stacked layer formed by stacking theinsulating film 4, the semiconductor layer 6 and the protective film 9in that order is interposed between a portion of the output terminal 12and the scanning signal line 2, but this stacked layer does not extendall of the way under the output terminal 12.

The reason for this construction is to enhance the corrosion-preventingeffect by covering the entire area of the scanning signal line 2 withthe stacked layer.

Embodiment 5

FIG. 6B is a view showing the construction of another embodiment of theliquid crystal display device according to the present invention, and isa view similar to FIG. 1. The construction of FIG. 6B differs from thatof FIG. 1 in that the stacked layer which covers the scanning signalline 2 is formed as a double layer made of two layers, i.e., theinsulating film 4 and the protective film 9. That is to say, thesemiconductor layer 6 is not used for preventing corrosion of thescanning signal line 2.

The reason for this construction is to ensure a sufficientcorrosion-preventing effect for the scanning signal line 2 by means ofthe stacked layer (double layer) made of the insulating film 4 and theprotective film 9, and to further improve the flatness at the locationwhere the sealing material 13 is formed.

Embodiment 6

FIG. 7 is a view showing the construction of another embodiment of theliquid crystal display device according to the present invention, and isa view similar to FIG. 1. The construction of FIG. 7 differs from thatof FIG. 1 only in that the semiconductor layer 6 from among theinsulating film 4, the semiconductor layer 6 and the protective film 9which cover the scanning signal line 2 is not formed at the locationwhere the sealing material 13 is formed. That is to say, thesemiconductor layer 6 is formed to extend only from outside the sealingmaterial 13 to the side of the driver IC 7A.

The reason for this construction is to obtain both the effect ofstrengthening the corrosion-preventing effect for the scanning signalline 2 and the effect of flattening the location where the sealingmaterial 13 is formed.

In each of Embodiments 2 to 6, reference has been made to a constructionin the vicinity of the driver ICs 7A connected to the scanning signallines 2. However, it goes without saying that a similar construction maybe provided in the vicinity of the driver ICs 8A connected to the videosignal lines 3.

In any of the above-described embodiments, each layer of the stackedlayer which covers the signal lines is made of the same material as apredetermined layer formed in each pixel area. However, this essentialto the invention, and the material need not be the same as the layerformed in each pixel area (a different material or a different processmay also be used).

Each of the aforesaid embodiments has been described on the basis of aso-called COG (chip-on-glass) type of liquid crystal display device inwhich drivers IC are mounted on a transparent substrate. However, itgoes without saying that the present invention is not limited to thistype. This is because the present invention can be applied to preventionof corrosion of signal lines in any case where the signal lines areformed over a surface area of a transparent substrate 1 to which thetransparent substrate 1B is not opposed.

In the above description of the embodiments, reference has been made toa liquid crystal display device which is a so-called vertical electricfield type represented by a TN (Twisted Nematic) type. However, it goeswithout saying that the present invention can also be applied to aliquid crystal display device of the lateral electric field type (or anIn-Plane-Switching type).

The lateral electric field type of liquid crystal display device isprovided with pixel electrodes and common electrodes which are disposedin the pixel areas of a liquid-crystal-side surface of one of the twotransparent substrates disposed so as to be opposed to each other with aliquid crystal interposed therebetween, the pixel electrodes and thecommon electrodes be spaced apart from each other, whereby the opticaltransmissivity of the liquid crystal is controlled by electric fieldsgenerated between these electrodes in parallel with the substrates.

The features of the above-described embodiments will be summarized inbrief as follows. If the present invention is to be employed, it isrecommended that a stacked layer, which covers signal fines that extendoutside of the area of a substrate that faces a liquid crystal (that issurrounded by a sealing material), which substrate is one of a pair ofsubstrates which constitute a liquid crystal display device, should beformed to extend from at least the area of the main surface of theaforesaid substrate that is opposed to the other of the pair ofsubstrates to an area opposed to the lower surface of the driver IC(particularly the lower surface located on the side the othersubstrate). It is also recommended that the stacked layer be made of atleast first and second insulating films (two kinds of insulating filmsformed by different processes) and preferably with a semiconductor layerinserted between these insulating films. Whether to expand this stackedlayer to a further extent can be appropriately determined according tothe combination conditions for the pair of substrates to be opposed toeach other and the durability of the stacked film.

As is apparent from the foregoing description, it is possible to preventcorrosion which occurs in signal lines which extend from inside asealing material outward thereof.

While we have shown and described several embodiments in accordance withthe present invention, it is understood that the same is not limitedthereto but is susceptible of numerous changes and modifications asknown to those skilled in the art, and we therefore do not wish to belimited to the details shown and described herein but intend to coverall such changes and modifications as are encompassed by the scope ofthe appended claims.

What is claimed is:
 1. A liquid crystal display device, comprising: apair of substrates disposed to oppose one another and fixed to oneanother by a sealing material maintaining a gap therebetween; a liquidcrystal area being formed by sealing a liquid crystal in the gap whichis surrounded by the sealing material; a plurality of pixel areas formedover a liquid-crystal-side surface of one of the pair of substrates inthe liquid crystal area; and a plurality of signal lines for supplyingsignals to the plurality of pixel areas respectively, said signal linesbeing formed over the liquid-crystal-side surface of said one of thepair of substrates and extending from the liquid crystal area to aperipheral portion of the liquid-crystal-side surface beyond the sealingmaterial; wherein at least one of the plurality of signal lines iscovered with a stacked layered structure at the peripheral portion ofthe liquid-crystal-side surface, and the stacked layered structure isformed by stacking a first insulating film, a semiconductor layer, and asecond insulating film on at least one of the plurality of signal linesin this order.
 2. A liquid crystal display device according to claim 1,wherein each of the plurality of pixel areas is provided with a thinfilm transistor formed of a semiconductor material and an insulatingmaterial and covered with a protective film, and the first insulatingfilm, the semiconductor layer and the second insulating film at theperipheral portion are made of materials identical to the insulatingmaterial and the semiconductor material of the thin film transistor, andthe protective film, respectively.
 3. A liquid crystal display deviceaccording to claim 1, wherein the stacked layer structure is formed toextend into the liquid crystal area inside the sealing material.
 4. Aliquid crystal display device according to claim 1, wherein the stackedlayer structure is formed within the peripheral portion of theliquid-crystal-side surface, has one of ends thereof opposite to an endof the other of the pair of substrates, and is extended along anextending direction of the at least one of the plurality of signal linesfrom the one of the ends thereof.
 5. A liquid crystal display deviceaccording to claim 4, further comprising a driver IC disposed on theperipheral portion of the liquid-crystal-side surface and having anoutput terminal connected to the at least one of the plurality of signallines, wherein the stacked layer structure has another of the endsthereof opposite to the driver IC.
 6. A liquid crystal display deviceaccording to claim 4, further comprising a driver IC disposed on theperipheral portion of the liquid-crystal-side surface and having anoutput terminal connected to the at least one of the plurality of signallines, wherein at least one portion of the stacked layer structure inthe peripheral areas is overlapped by the driver IC.
 7. A liquid crystaldisplay device according to claim 1, wherein the stacked layer structureis formed to be extended to a halfway portion below the sealingmaterial.
 8. A liquid crystal display device according to claim 5,further comprising a driver IC disposed on the peripheral portion of theliquid-crystal-side surface and having an output terminal connected tothe at least one of the plurality of signal lines, wherein the stackedlayer structure has another of the ends thereof opposite to the driverIC.
 9. A liquid crystal display device according to claim 1, furthercomprising a drive IC mounted on the peripheral portion of theliquid-crystal-side surface, wherein one end of the at least one of theplurality of signal lines which extends at the peripheral portion of theliquid-crystal-side surface is connected to an output terminal of thedriver IC, and the stacked layer structure is formed to extend into aportion below the driver IC.
 10. A liquid crystal display deviceaccording to claim 1, further comprising a driver IC mounted on theperipheral portion of the liquid-crystal-side surface, wherein one endof the at least one of the plurality of signal lines which extends atthe peripheral portion of the liquid-crystal-side surface is connectedto an output terminal of the driver IC, and the stacked layer structureis formed to extend into a halfway position below the output terminal.11. A liquid crystal display device according to claim 1, furthercomprising a driver IC disposed on the peripheral portion of theliquid-crystal-side surface and having an output terminal connected tothe at least one of the plurality of signal lines, wherein at least oneportion of the stacked layer structure is overlapped by the driver IC.12. A liquid crystal display device according to claim 1, wherein atleast one of the plurality of signal lines is covered with a stackedlayer structure at the pixel areas which is formed by stacking the firstinsulating film and the second insulating film on the at least one ofthe plurality of signal lines in this order.
 13. A liquid crystaldisplay device according to claim 12, wherein each of the plurality ofpixel areas is provided with a thin film transistor formed of asemiconductor material and an insulating material, and covered with aprotective film, and the first insulating film, the semiconductor layerand the second insulating film at the peripheral portion are made ofmaterials identical to the insulating material and the semiconductormaterial of the thin film transistor, and the protective film,respectively.
 14. A liquid crystal display device according to claim 12,further comprising a driver IC disposed on the peripheral portion of theliquid-crystal-side surface and having an output terminal connected tothe at least one of the plurality of signal fines.
 15. A liquid crystaldisplay device according to claim 1, wherein in at least a portion ofthe region of the sealing material, the at least one of the plurality ofsignal lines is covered with the second insulating film without at leastone of the semiconductor layer and the first insulating layer.